DE69302443T2 - Control device for several hydraulic consumers - Google Patents

Description

The invention relates to a control unit for a plurality of hydraulic consumers, through which the consumers are supplied from the same pressure fluid source, each being connected via a proportional distributor.

It is known that directional control valves are devices that are placed between a pressure fluid generator and a consumer in order to control the latter's operation by changing the type of connection with the pressure fluid generator.

The proportional type directional control valves not only have a control spool whose position determines the cross-section of a throttle point, but also an automatic compensating spool to keep the difference in pressure upstream and downstream of this throttle point constant so that a given position of the control spool corresponds to a certain pressure fluid flow. Therefore, when a consumer is controlled by a proportional directional control valve, its operating speed is determined by the position of the control spool, regardless of the load on the consumer.

If the pressure fluid generator supplies a number of consumers, each of which is assigned a proportional directional control valve, it can happen that the total amount of pressure fluid required by the consumers exceeds the maximum volume that the pressure fluid generator can supply. The respective compensating slides are then no longer able to keep the difference in pressures upstream and downstream of the throttle point at the predetermined constant value in each of the directional control valves, so that the most heavily loaded consumers slow down or stop, while those with less stress can continue to function.

In order to avoid these discrepancies, it has already been proposed that the pressure fluid generator be regulated in dependence on the required power. This is currently provided for in most hydraulic controls where the pressure fluid generator supplies a number of consumers. The regulation is implemented in the form of load sensing means, called "load-sensing", which supply the pressure fluid generator with the pressure of the consumer with the highest load, to which it reacts by generating an operating pressure that is equal to the pressure of the load signal (load-sensing) plus a constant. In practice, this constant is added as long as the total demand for pressure fluid is less than the quantity that can be supplied, but if the demand exceeds this, the value added to the load signal is less than the constant, and the smaller the value the greater the excess of the quantity of pressure fluid requested. It is this reduction in the added value that is used to avoid the aforementioned discrepancies.

FR-A-2.339.757 proposes to act on the actuating pressure of the control slide in each of the proportional distributors by providing that the actuating valves are no longer supplied directly by a control pump, but rather a limiting valve is interposed between the pump and the actuating valves, which changes the supply pressure of the control valves according to the difference between the pressure of the pressure fluid generator and the load signal (load-sensing). As long as the pressure generator is functioning normally, the supply pressure remains of the control valves is just as constant as if these valves were supplied directly by the control pump. In the event of an excessive demand for pressurized fluid, the supply pressure of the control valves is reduced in proportion to the excess of the demand, the actuating pressure of all the control spools being reduced to the same extent and, as a result, the throttling produced by the control spools is increased in the same way, with the result that each distributor reduces the flow in the same proportion, so that all consumers are slowed down while maintaining their speed ratios.

In order to achieve the same result in the case where proportional distributors have a compensating valve upstream of the control valve, FR-A-2.548.290 proposes to act on the actuating means of the compensating valve: it is still urged by the pressure upstream of the control valve in the closing direction and by the pressure downstream of the control valve in the opening direction, but the traditional spring is replaced by a double pressure actuation, in the closing direction by the pressure signal pressure (badsensing) and in the opening direction by the pressure of the pressure fluid generator. The difference in pressures upstream and downstream of the control valve gap is thus subject to the difference between the pressure of the pressure fluid generator and the pressure of the load signal, which leads to the above-mentioned result.

The invention is based on the object of obtaining the same result but with an improved effect.

For this purpose, a control unit for a plurality of hydraulic consumers, through which the consumers are supplied from the same pressure fluid source, is by connecting each one via a proportional distributor, proposed with:

- a control slide, the position of which determines the cross-section of a first control gap,

- a compensating slide for regulating the difference between the pressures upstream and downstream of the first control gap by providing a second control gap with a suitable cross-section in the flow direction upstream of the first control gap, and

- actuating means for the compensating slide to allow it to automatically assume a position in which it provides the second control gap with a suitable cross-section as a function of several pressures acting in the opening direction or in the closing direction,

which control unit is characterized in that it has means for detecting the highest of the pressures prevailing in the various proportional distributors in the direction of flow upstream of the first control gap and that in each of the proportional distributors the actuating means of the compensating slide cause it to react to the highest of the upstream pressures detected in this way.

These features result in a particularly short response time of the compensating slide, especially in comparison with the aforementioned state of the art, because the maximum value of the pressures in front of the respective first control gap is higher than the pressure of the load signal (load-sensing).

In a first preferred embodiment of the invention, in each proportional distributor the actuating means of the compensating slide are designed such that it

- is forced in the opening direction by the control gap behind the first control gap in the flow direction prevailing pressure and the pressure prevailing in the flow direction upstream of the second control gap and

- is urged in the closing direction by the pressure before the first control gap, the highest of the pressures before the respective first control gap and an essentially constant force,

the control unit thus being applicable to a pressurized fluid source which generates a working pressure which is normally equal to a regulated pressure requested in accordance with a load sensing, increased by a constant.

It will be noted that it is essential that in each distributor the compensating slide is subjected to a force in the closing direction: this force causes the compensating slide to close completely when the demand for pressure fluid is too great to maintain all the speed ratios between the consumers, which means that all consumers are then stopped (there is no more pressure fluid when the compensating slide is closed)

Preferably, the actuating means for the compensating slide have a first control surface on the compensating slide, which is subjected to the pressure behind the first control gap, a second control surface, which is subjected to the pressure in front of the second control gap, a third control surface, which is subjected to the pressure in front of the first control gap and a fourth control surface, which is subjected to the highest of the pressures in front of the first control gaps, the first and second control surfaces being directed opposite to the third and fourth control surfaces, as well as a spring which loads the compensating slide in the closing direction.

In a second preferred embodiment, the control unit has at least one auxiliary valve which is fed by the pressure fluid source and generates a pressure which is normally equal to the highest pressure prevailing in front of the respective first control columns, increased by a constant, wherein in each proportional distributor the actuating means for the compensating slide are designed in such a way that it:

- is forced in the opening direction by the pressure behind the first control gap and the pressure generated by the auxiliary valve and

- is forced in the closing direction by the pressure in front of the first control gap, the highest of the pressures in front of the first control gaps and by an essentially constant force.

This second embodiment differs from the first by the presence of the auxiliary valve, the pressure generated by it being used instead of the pressure upstream of the second control gap. This makes it possible to avoid the difficulties that arise when the pressure upstream of the second control gap is not the same due to different pressure losses between the pressure fluid generator and the individual distributors in the latter.

In addition, this embodiment offers the advantage of achieving the desired result even if the pressure fluid generator is not regulated as a function of the loads of the consumers.

Preferably, it is provided that in each proportional distributor the actuating means for the compensating slide have a first control surface acted upon by the pressure behind the first control gap, a second control surface acted upon by the pressure behind the first control gap, the control surface acted upon by the pressure generated by the auxiliary valve, a third control surface acted upon by the pressure upstream of the first control gap and a fourth control surface acted upon by the highest pressure prevailing upstream of the respective first control gaps, wherein the first and second control surfaces are directed opposite to the third and fourth control surfaces, and a spring loading the compensating slide in the closing direction.

Preferably, for reasons of simplification, the first and third control surfaces of the compensating slide are of equal dimensions and the second and fourth control surfaces of the compensating slide are of the same size.

In a further preferred embodiment, the auxiliary valve

- a supply chamber connected to the pressure fluid source,

- a control chamber in which the highest pressure prevails before the respective first control columns,

- an outlet chamber in which the generated pressure prevails,

- a slide valve, the position of which determines the cross-section of a control gap between the supply chamber and the outlet chamber and which has a first control surface located in the control chamber in such a way that the highest of the pressures prevailing in front of the respective first control gaps acts in the opening direction, and a second control surface located in the outlet chamber in such a way that the pressure generated acts in the closing direction, and

- a spring that acts on the slide in the opening direction.

In the case where the proportional distributors are divided into several groups consisting of one or more adjacent distributors which are arranged at a distance from one another, the control unit preferably has an auxiliary valve arranged adjacent to each group.

This avoids the problems associated with pressure losses in the line and, above all, the need to provide a line between the auxiliary valve and a group of distributors located at a distance from it.

Preferably, the proportional distributors are designed without check valves between the second and the first control gap.

In fact, the invention, at least in the two above-mentioned embodiments, makes the check valves provided in all previous proportional distributors unnecessary. This is due to the fact that it is certain that in the rest state (when all the control slides are in the neutral position), all the compensating slides are closed: if one adds up and compares all the forces acting in the closing direction and all the forces acting in the opening direction, taking into account that in the rest state the pressure behind each compensating slide is equal to the pressure in front of it (even if the compensating slide is closed due to unavoidable small losses), one sees that the forces acting in the closing direction are always greater than the forces acting in the opening direction.

In a further preferred embodiment of the invention, the means for detecting the highest of the respective first control columns, a common line closed at a first end, which opens into the pressure fluid reservoir at the other end via a throttle point, and a check valve for each proportional distributor, which can be opened from the supply line to the first control column to the common line. These features actually have a positive effect on the reaction speed of the compensating slide.

The description of the invention will be continued below with the description of embodiments which are given for explanatory purposes and are not to be understood as limiting, with reference to the accompanying drawings.

Show it:

Fig. 1 shows a simplified section through a proportional distributor which is part of a control unit according to the invention;

Fig. 2 is a diagram of a hydraulic circuit with such a control unit with two distributors connected at their ends according to Fig. 1 and

Fig. 3 and 4 show a modified embodiment in views corresponding to Fig. 1 and 2.

The directional control valve 70 shown in Fig. 1 is similar to that described in French patent FR-B-25 62 632, with the exception of its pressure compensation device.

It has a stator body 1 in which a cylindrical control slide 3 slides in a bore 2. As usual, the change in the hydraulic circuit is brought about by moving grooves of the slide 3 in front of recesses in the stator.

At its left end, in the example, the slide 3 is provided with a known resilient return device, which includes a coil spring 4 clamped between shoulders 5 and 6 of two bushes 7 and 8, which are held between two shoulders of the end of the slide 3 designated 9, around which they can slide. In this way, the slide 3 is automatically returned to a neutral rest position, whereas it is pushed to the right (Fig. 1) when a control pressure is directed into an opening 10 of a fixed cap 61. Conversely, the slide 3 is displaced to the left when a control pressure on the opposite side is directed into an opening 11 of a cap 62 at its other end. In the embodiment shown, it has been assumed that the three-position slide 3 is used to control a double-acting hydraulic power cylinder 12. For this purpose, one side of the power cylinder 12 is connected to a first supply channel 13 in the stator 1, while the other side of the power cylinder 12 is connected to a second supply channel 14 of the stator 1.

The directional control valve receives the pressure fluid supplied by a pressure fluid generator 71 in an annular chamber 15.

The supply chamber 15 surrounds a cylindrical compensating slide 16, which is also referred to as a balancer and is displaceable in a bore 80 of the stator 1. and which has a groove 81 which, depending on the position of the slide 16, creates a more or less large control gap between the chamber 15 and an annular chamber 27 surrounding the central part of the control slide 3.

At each of its two ends, the control slide 3 has an inner axial recess, which is designated 28 on the left and 29 on the right.

The recess 28 communicates with the outside of the valve through two radial holes 30 and 31 respectively. In the same way, the recess 29 opens into two radial holes 32 and 33. When the valve 3 is in its neutral rest position, the hole 30 faces a flat section 34 between two annular chambers 35 and 36 which closes it. The chamber 35 communicates with the first supply channel 13, while the chamber 36 is connected to the return line.

Similarly, the bore 32 is closed in the rest position by a flat section 37 between two annular chambers 38 and 39. The chamber 38 is connected to the second supply channel 14, while the chamber 39 is connected to the return.

Between the bores 30 and 31, the stator forms a flat section 40 at the bore, in front of which a groove 41 in the slide 3 is movable.

When the slide 3 has been displaced to the right (Fig. 1), an annular chamber 42 in the stator extends around the slide 3 in the zone surrounding the bore 31.

In the same way, the slide 3 has a groove 43 at its opposite end, which is movable in front of a flat section 44 of the stator. An annular chamber 45 in the stator extends around the bore 33 when the slide 3 is pushed back to the left.

The two chambers 42 and 45 are connected by a channel 46, which is referred to as the load sensing channel.

Progressive control edges are provided on the various grooves of the slide, as indicated, for example, by the reference numerals 48, 49, 50, 51.

Finally, a first filling valve 52 is mounted parallel to the first supply channel 13. In the same way, a filling valve 53 is mounted parallel to the second supply channel 14. Behind the valves 52 and 53 there is a chamber 54 connected to the oil return.

A pressure relief valve 55 or 56 is provided on the side of each supply channel 13, 14, which thus have an outflow to the return chambers 36 or 39.

The functionality of the control slide 3 is described below.

In the neutral position, the chambers 27, 35 and 38 are closed so that the power cylinder 12 is held immobile because no pressure fluid flows to the consumer. In addition, the channel 46 is connected to the chamber 36 or 39 via the grooves 41 and 43, i.e. it is connected to the return line.

When the opening 10 is subjected to a control pressure, as is the case according to Fig. 1, the slide 3 slides a distance to the right, the size of which is determined by the control pressure, which comes into equilibrium with the counterpressure of the more or less compressed spring 4. The supply pressure of the chamber 27 reaches the channel 13 via the groove 49 and the chamber 35, while the channel 14 is connected to the return chamber 39 via the groove 51. Each of the grooves 49 and 51 defines a control gap, the cross-section of which depends on the position of the slide 3. Furthermore, the channel 46 on the left side communicates with the channel 13 via the channels 31, 28 and 30, while the channel 46 on the right side is closed. The pressure behind the control gap formed by the groove 49 is thus transferred to the channel 46.

When a control pressure is applied to the opening 11, the slide 3 slides to the left to a position which is determined by the magnitude of the control pressure. The supply pressure from the chamber 27 reaches the channel 14 via the groove 50 and the chamber 38, while the channel 13 is connected to the return chamber 36 via the groove 48. Each of the grooves 48 and 50 forms a control gap whose cross-section is determined by the position of the slide 3. Furthermore, the channel 46 on the right-hand side communicates with the channel 14 via the bores 33, 29 and 32, while the channel 46 on the left-hand side is closed. The pressure behind the control gap formed by the groove 50 is thus transferred to the channel 46. It can therefore be seen that in the neutral position the channel 46 is subjected to the pressure of the return line, while in every working position it is subjected to the pressure behind the control gap formed by the slide 3 in the supply line of the power cylinder 12, ie its supply pressure.

The circuit selection switch 99 (with the "OR" function) communicates with channel 46 via one of its inputs and a channel 72. Its other input is connected via a channel 73 to the output channel of a circuit selection switch of a similar directional control valve. In the present example, the pressure in channel 46 is the highest, so that the circuit selection switch 99 assumes the position shown, in which it transmits the supply pressure of the power cylinder 12, which is the highest supply pressure of the totality of consumers supplied by the pressure fluid generator 71, to a channel 74 via its output. In general, as can be clearly seen from Fig. 2, it can be stated that channel 74 is always subjected to the pressure of the consumer with the highest load. This pressure, referred to as the load signal, is passed on to the pressure fluid generator 71, which then generates an operating pressure which is normally equal to the pressure of the load signal plus a constant.

In the position shown in Fig. 1, the compensating slide 16 closes the connection between the chambers 15 and 27, but if it is moved to the left, it creates, depending on its position, a more or less large control gap in the supply line of the power cylinder 12 in the flow direction upstream of the control gap formed by the slide 3.

The compensating slide 16 has a first piston surface 82 which is exposed to the pressure behind the control gap formed by the control slide 3, a second piston surface 83 which is exposed to the pressure in front of the control gap formed by the compensating slide 16. a third piston surface 34 which is exposed to the pressure in front of the control gap formed by the control slide 3, and a fourth piston surface 85 which is subjected to the pressure prevailing in a chamber 86 arranged to the left of the compensating slide.

The piston surfaces 82 and 83 point to the right and are opposite to the piston surfaces 84 and 85, which point to the left. Since the control slide 16 closes the control gap it forms when it moves from left to right and vice versa, the pressures acting on the piston surfaces 82 and 83 urge the compensating slide 16 in the opening direction, while the pressures acting on the piston surfaces 84 and 85 urge it in the closing direction. A spring 87 is provided in the left-hand chamber 86 between its bottom and the piston surface 85, whereby the compensating slide 16 is still urged in the closing direction by an essentially constant force. In order to adjust it, a screw 88 is provided, which forms the bottom of the chamber 86.

The piston surface 82 is exposed to the pressure prevailing behind the control gap created by the control slide 3 because it is located in a chamber 89 connected to the channel 46 via a channel 90, and the piston surface 84 is exposed to the pressure prevailing in front of the control gap created by the control slide 3 because it is located in a chamber 91 connected to the chamber 27 via a channel 92.

The compensating slide 16 is provided with a radial bore 93 which is connected to an axial blind bore 94 which has its mouth in a seat surface which can be closed or released by a ball, the return spring 96 of which is clamped in a chamber 98 which opens into the chamber 86 via an axial opening 100. The latter is connected via a channel 101 to a channel 102 which is closed at one end and opens at the other end via a throttle point 104 into the reservoir of the pressure fluid generator, the channel 102 being common to all directional control valves which are connected to it with their chamber corresponding to the chamber 86.

Fig. 2 shows a control unit according to the invention, which consists of a single group of two interconnected directional control valves, namely the directional control valve 70 shown in Fig. 1 and an identical directional control valve 70', all parts relating to this having the same reference numerals as for the directional control valve 70, but with an added index line.

It can be seen that for each directional control valve 70 and 70', the common line 102 is connected upstream of the control gap formed by the control slide 3 via a check valve, the ball 95 of which forms the closing body and which is permeable in the direction of the channel 102. The highest of the pressures prevailing upstream of the control gaps formed by the slides 3 and 3' therefore prevails in the channel 102. The throttle point 104 causes the line 102 to relax, which allows it to be constantly adjusted to the maximum of the pressures upstream of the slides 3 and 3'. It is therefore this latter pressure that prevails in the chamber 86 and in the corresponding chamber of the directional control valve 70'.

In the embodiment shown, the piston surfaces 82 and 84 have the same surface size S₂ and the piston surfaces 83 and 85 have the same surface size S₁. If one continues where F is the force exerted by the spring 87, MAX(Pi) is the pressure prevailing in front of the control gap formed by the control slide 3, MAX(Pi) is the maximum value of the pressures prevailing in front of the control gap formed by the control slide, PUi is the pressure prevailing behind the control gap formed by the control slide 3 and P is the pressure prevailing in front of the control gap formed by the compensating slide 16, the equation is obtained:

Pi - PUi = S₁/S₂ [P-MAX(Pi)] - F/S2

It can be seen that the pressure difference Pi - PUi depends on the pressure difference P - MAX(Pi) in the form of a linear function with always positive coefficient and always negative constant.

Given the way in which the pressure fluid generator is controlled, the pressure difference P - MAX(Pi) remains constant as long as the pressure fluid generation can satisfy the total demand for pressure fluid, while this pressure difference is smaller than this constant when the demand for pressure fluid predominates, the reduction being greater the more the demand predominates.

The sizes S₁, S₂ and F are chosen in particular depending on the following requirements:

- the compensating slide 16 should, in normal operation, where P - MAX(Pi) = a, ensure a value b for Pi - PUi such that:

b = S₁/S₂ a - F/S2;

- the compensating slide 16 should close at a certain minimum value c of P - MAX(Pi), from which it is assumed that the overload is too great to be able to maintain the speed ratios between the consumers, such that:

S1 c = F

It will be noted that there is no check valve in the directional control valve 70 between the chambers 15 and 27, in contrast to conventional proportional directional control valves in which a check valve is always provided which is permeable from the control gap formed by the compensating slide to the control gap formed by the control slide.

Thus, in the control unit, it is certain that in the resting state, when all control slides 3 are in the neutral position, all compensating slides 16 are in the closed position shown: if one retains the same designations as above and takes into account that in the resting state Pi = P in all directional control valves, even if the compensating slide 16 is closed due to unavoidable, small losses between the inlet and outlet sides, one can see that the compensating slide 16 is urged in the closing direction by:

F + PS₁ + PS₂

and in the opening direction by:

PS1;.

Since F + PS2 is always positive, it is clear that the forces acting in the closing direction are always greater than those acting in the opening direction.

In a variant of the invention not shown, the pressure MAX(Pi) prevailing in the channel 102 is used to regulate the pressure fluid generator, instead of the pressure of the load signal prevailing in the channel 74. This variant is less interesting than the one shown, since it is not so easy to regulate a pressure fluid generator when the difference between the control pressure and the operating pressure becomes very small.

In other variants not shown, the load detection with circuit selection switches is replaced by a load detection with check valves or the device for determining MAX(Pi) with check valves is replaced by a sensing device with circuit selection switches.

However, the solution shown, where the pressure of the load signal (load-sensing) is determined by circuit selector switches, while the MAX(Pi) is determined by check valves, seems to be preferable, since fast response times are desirable for the compensating slide 16 (in order to react very quickly to any changes in the load), while it is better to have slow response times for the control of the pressure fluid generator (in order to avoid constant changes in its operating mode).

It will be noted that the channels 73 and 74 together with the selector switch 99 form a unit traversing the entire directional control valve 70 and that the same also applies to the channel 102, so that it is possible to connect the between the directional control valves by simply connecting their ends to each other, which is fully illustrated in Fig. 2.

In the illustration of the embodiment of the control unit according to the invention according to Fig. 3 and 4, the same reference numerals have been retained for matching parts, while the number 100 has been added to the reference numerals for corresponding parts.

The proportional directional control valve 170 according to Fig. 3 has a compensating slide 116, the right-hand part of which is different from that of the compensating slide 16: opposite the piston surface 83 it has a piston surface 300 with the same effective area, i.e. S₁, a further piston surface 301 is subjected to the pressure behind the control gap formed by the control slide, and yet another piston surface 302 is subjected to the pressure generated by an auxiliary valve 303.

The piston surfaces 301 and 302 point to the right and are thus opposite to the piston surfaces 84 and 85, so that the pressures acting on them force the compensating slide 116 in the opening direction.

The piston surface 301 is subjected to the pressure prevailing behind the control gap formed by the control slide 3 because it is located in the channel 146, and the piston surface 302 is exposed to the pressure generated by the valve 303 because it is located in a chamber 304 connected to the valve 303 via a channel 305.

The piston surface 301 has an area equal to the piston surface 84, ie S₂, and the piston surface 301 has an effective area equal to the piston area 85, ie S₁.

Since the piston surfaces 83 and 300 are also of equal size, the pressure prevailing in the chamber 15 has no influence on the position assumed by the compensating slide 116.

Taking into account the arrangement and dimensioning of the piston surfaces 301 and 302, the effect of the pressure in front of the control gap formed by the compensating slide has been replaced by the effect of the pressure generated by the additional valve 303.

If one takes into account the changes in the designations, the equations given above are also applicable to the variant shown in Fig. 3 and 4.

The auxiliary valve 303 has a stator body 306 which delimits a supply chamber 307 which is connected to the outlet opening of the pressure fluid generator 71, a control chamber 308 in which the pressure MAX(Pi) prevails, an outlet chamber 309 in which the generated pressure prevails, a slide 310 whose position determines the cross-section of a control gap between the chambers 307 and 309 by means of a groove 311, and a spring 312 which acts on the slide 310 in the opening direction, a screw 313 being provided to adjust the force with which the spring acts.

The pressure MAX(Pi) prevails in the chamber 308 because this chamber is connected to the channel 102. The slide 310 has a first piston surface 314 which is located in the chamber 308 and is therefore exposed to the pressure MAX(Pi) in the opening direction. It also has a second piston surface 315, which is located in the chamber 309, so that the pressure generated acts on the piston surface 315 in the closing direction.

It turns out that in the case where the effective area of the piston surfaces 314 and 315 is equal and this is denoted by S, the pressure generated by P and the force exerted by the spring by F, we obtain:

Pp = MAX(Pi) + F/S

The pressure generated is thus independent of the pressure provided by the pressure fluid generator. This makes it possible to avoid the difficulties that could be encountered in the embodiment according to Figs. 1 and 2 due to the fact that, in certain proportional directional control valves, different pressures occur upstream of the control gap formed by the compensating slide, in particular when these directional control valves are located at different distances from the pressure fluid generator and therefore there are different pressure losses between the delivery pressure of the pressure fluid generator and the pressure prevailing in the chamber designated 15.

If the proportional directional control valves of the control unit are divided into several groups of one or more adjacent directional control valves and the groups are spaced apart from each other, e.g. in a public service vehicle divided into a first group of two directional control valves controlling the right and left motors for the forward movement of the vehicle, a second group with a single directional control valve controlling the rotary movement of a turret structure, and a third group with several In the case of directional control valves controlling the various arms of the vehicle, it is preferable to provide an auxiliary valve for each of the groups, not only to avoid problems due to pressure losses, but also to avoid having to provide lines between a central auxiliary valve and the various groups.

The maintenance of the speed ratios between the consumers is similar to that of the control unit shown in Fig. 1 and 2, because in case of excessive demand for pressure fluid, the chamber 307 is not supplied with a pressure sufficient to add F/S to MAX(Pi), but rather only a smaller value is added, which is smaller the greater the excess demand for pressure fluid.

The various comments in connection with the embodiment according to Figs. 1 and 2, in particular those concerning possible variants, are also applicable to the embodiment according to Figs. 3 and 4.

In a variation of this latter embodiment (not shown), the auxiliary valve generates a pressure that is normally equal to the pressure of the load signal (badsensing), increased by a constant, the connection of the chamber 308 to the channel 102 being replaced by a connection to the channel 744. In this case, the determination of the maximum value of the pressures upstream of the control gap formed by the control slide can be suppressed and the pressure of the load signal (load-sensing) can be allowed to prevail in the chamber 86. It is also possible, depending on the circumstances, to select a control pressure other than MAX(Pi) or the pressure of the load signal. Even in these variations, the advantages gained by using an auxiliary valve are retained.

In general, numerous modifications can be made to the embodiments described. In this respect, it should be remembered that the invention is not limited to the latter.

Claims (14)

1. Control unit for a plurality of hydraulic consumers (12, 12'), through which the consumers are supplied from the same pressure fluid source (71) by each being connected via a proportional distributor with - a control slide (3), the position of which determines the cross-section of a first control gap, - a compensating slide for regulating the difference between the pressures upstream and downstream of the first control gap by providing a second control gap with a suitable cross-section in the flow direction upstream of the first control gap, and - actuating means for the compensating slide to allow it to automatically assume a position in which it provides the second control gap with a suitable cross-section as a function of several pressures acting in the opening direction or in the closing direction, characterized in that it has means (95, 95', 102, 104) for detecting the highest of the pressures prevailing in the various proportional distributors (70, 70'; 170, 170') in the flow direction upstream of the first control gap and that in each of the proportional distributors the actuating means of the compensating slide (16, 116) cause it to react to the highest of the upstream pressures thus detected. 2. Control unit according to claim 1, characterized in that in each proportional distributor (70, 70') the actuating means of the compensating slide (16) are designed in such a way that it - is urged in the opening direction by the pressure prevailing in the flow direction behind the first control gap and the pressure prevailing in the flow direction in front of the second control gap and - is urged in the closing direction by the pressure before the first control gap, the highest of the pressures before the respective first control gap and an essentially constant force, the control unit being thus applicable to a pressurized fluid source (71) which generates a working pressure which is normally equal to a controlled pressure requested in accordance with a load sensing, increased by a constant. 3. Control unit according to claim 2, characterized in that in each proportional distributor the actuating means for the compensating slide comprise: on this a first control surface (82) subjected to the pressure behind the first control gap, a second control surface (83) subjected to the pressure in front of the second control gap, a third control surface (84) subjected to the pressure in front of the first control gap and a fourth control surface (85) subjected to the highest of the pressures in front of the first control gaps, the first and second control surfaces (82, 83) being directed opposite to the third and fourth control surfaces (84, 85), as well as a spring (87) which loads the compensating slide (16) in the closing direction. 4. Control unit according to claim 1, characterized in that it comprises at least one auxiliary valve (303) fed by the pressure fluid source (71) and generating a pressure which is normally equal to the highest in front of the respective first control columns, increased by a constant pressure, and that in each proportional distributor (170, 170') the actuating means for the compensating slide are designed such that it: - is forced in the opening direction by the pressure behind the first control gap and the pressure generated by the auxiliary valve (303) and - is forced in the closing direction by the pressure in front of the first control gap, the highest of the pressures in front of the first control gaps and by an essentially constant force. 5. Control unit according to claim 4, characterized in that in each proportional distributor the actuating means for the compensating slide have a first control surface (301) subjected to the pressure behind the first control gap, a second control surface (302) subjected to the pressure generated by the auxiliary valve, a third control surface (84) subjected to the pressure in front of the first control gap and a fourth control surface (85) subjected to the highest pressure prevailing in front of the respective first control gaps, the first and second control surfaces (301, 302) being directed opposite to the third and fourth control surfaces (84, 85), as well as a spring (87) loading the compensating slide (116) in the closing direction. 6. Control unit according to one of claims 3 or 5, characterized in that the first and the third control surface (82, 84; 301, 84) of the compensating slide (16, 116) are of equal dimensions, and that the second and the fourth control surface (83, 85; 302, 85) of the compensating slide has the same size. 7. Control unit according to one of claims 4 to 6, characterized in that the auxiliary valve (303) comprises: - a supply chamber (307) connected to the pressure fluid source (71), - a control chamber (308) in which the highest of the pressures prevails in front of the respective first control columns, - an outlet chamber (309) in which the generated pressure prevails, - a slide (310), the position of which determines the cross-section of a control gap between the supply chamber (307) and the outlet chamber (309) and which has a first control surface located in the control chamber (308) such that the highest of the pressures prevailing in front of the respective first control gaps acts in the opening direction, and a second control surface (315) located in the outlet chamber (309) such that the generated pressure acts in the closing direction, and - a spring (312) acting on the slide (310) in the opening direction. 8. Control unit according to one of claims 4 to 7, characterized in that the proportional distributors are divided into several groups consisting of one or more adjacent distributors, which are arranged at a distance from one another, and that for each group it has an auxiliary valve arranged adjacent to it. 9. Control unit according to one of claims 2 to 8, characterized in that the proportional distributors (70, 70', 170, 170') without check valves between the second and the first control gap. 10. Control unit according to one of claims 1 to 9, characterized in that the means for detecting the highest of the pressures prevailing in front of the respective first control gaps comprise a common line (102) closed at a first end, which opens into the pressure fluid reservoir at the other end via a throttle point (104), and a check valve (95, 95') for each proportional distributor, which can be opened from the supply line to the first control gap to the common line. 11. Control unit according to one of claims 1 to 10, characterized in that it has load sensing (“badsensing”) load detection means (73, 74, 99, 99') which supply the pressure of the most heavily loaded consumer to the pressure fluid source (71). 12. Control unit according to claim 11, characterized in that the load detection means for each proportional distributor have a line which connects the line behind the first control gap to a selection switch (99, 99') for selecting a circuit, and that in the case of several circuit selection switches, these are arranged in a cascade. 13. Control unit according to one of claims 1 to 12, characterized in that each proportional distributor has a housing (1) with lines (73, 741 102) which extend completely through the housing in such a way that the distributors can be connected in a simple manner with their ends lying against one another. 14. Control unit according to claim 10 in combination with claims 3 or 5, characterized in that each proportional distributor has a housing with lines (73, 74, 102) which pass completely through it in such a way that the distributors can be connected with their ends adjacent to one another, and that the check valve, which opens from the supply line to the first control gap to the common line, is accommodated between the third control surface (84) and the fourth control surface (85) in the compensating slide (16).